1. Field of the Invention
The present invention relates to a gain compensation circuit, and more particularly to a gain compensation circuit applied to an outdoor microwave transceiver.
2. Description of the Related Art
Generally, the gain of a normal transceiver will decrease when it is operated at high temperature (about 40° C. to 60° C.), but increase at low temperature (below about 20° C.). Therefore, for some outdoor satellite transceivers which often operate in suboptimal environmental conditions, unless some gain compensation addressing temperature variation is performed, the gain of the transceiver will vary with the environmental temperature, causing signal distortion, and deteriorating communication quality. Therefore, it is common practice to design a compensation circuit which is able to suppress the gain of the transceiver at low temperature but enhance the gain of the transceiver at high temperature.
As far as the gain compensation of the outdoor transceiver is concerned, a passive attenuator cooperating with a thermistor is commonly used to act as a gain compensation mechanism of the transceiver. However, such structure will degrade the quality of noise figure of the transceiver due to gain attenuation. Another known method is to use a special feature of gain relating to temperature of an active amplifier to achieve the effect of gain compensation. However, this has the drawback of a high material cost.